Radiolarian biostratigraphic correlation around the Jurassic–Cretaceous boundary between the Alpine Tethys and the Pacific

In setting up the Global Boundary Stratotype and Section (GSSP) for the Jurassic–Cretaceous boundary (JKB), the Berriasian Working Group (BWG) of the International Subcommission on Cretaceous Stratigraphy recommends to shift down the JKB to an interval between the paleomaginetic M20n1r and the base of M19r. The BWG is discussing markers defining the JKB. Radiolarians are one of ideal candidates for defining the JKB because they are wide spread and can be found in both shallow and deep marine sedimentary facies worldwide. The JKB lies around the base of the Unitary Association Zone (UAZ) 13 and within the Pseudodictyomitra carpatica Zone. Our radiolarian biostratigraphic research around the JKB in two Itarian sections, Torre de’Busi (Lombardian Basin) and Bosso Valley (central Apennines), and at ODP Site 801 in the western Pacific enables to correlate these sections by means of radiolarians.

The Torre de’Busi and Bosso Valley sections are strong GSSP candidates in the Alpine Tethys. The Maiolica Formation, which includes the JKB at the lowermost part, is characterized by whitish beige to gray colored, well-bedded micritic limestones with abundant black to gray chert layers and nodules. Integrated calcareous nannofossil, calpionellid, magnetostratigraphic, and cyclostratigraphic investigations provide a reliable stratigraphic framework for the Torre de’Busi section. Calpionellid biostratigaraphic and magnetostratigraphic study was conducted in the Bosso Valley section. A total of 49 samples in the Torre de’Busi section and 47 samples in the Bosso Valley section have been collected for our radiolarian biostratigraphic study across the JKB. In the Torre de’Busi section only horizons corresponding to the lower part of M20 contain moderately preserved radiolarians. In the Bosso Valley section several horizons corresponding to the interval between the M20n1r and the base of M19r yielded moderately to well preserved radiolarians.

Radiolarian biostratigraphy accross the JKB in the western Pacific was studied at ODP Site 801. The Pseudodictyomitra carpatica Zone is recognized in a radiolarite sequence from Core 15 to Core 20 at the site. Radiolarian markers for delimimating the JKB can be selected among taxa of which first occurrence is recorded in the UAZ 13. The result of a radiolarian biostratigraphic correlation between Alpine Tethys sections and western Pacific sections is presented. Candidates of radiolarian markers for the JKB are discussed. They are included in the genera Cinguloturris, Hemicryptocapsa, Hsuum, Loopus, Pantanellium, Vallupus, and Zhamoidellum.